The present invention relates to an apparatus and method for machining features in sheets of material, and more particularly, relates to an apparatus and method which are simple in use and flexible in operation.
In the current manufacture of multilayer ceramic (MLC) substrates for integrated circuit semiconductor package structures, a plurality of ceramic sheets is formed by doctor blading a slurry containing a resin binder, a particulate ceramic material, solvents, and a plasticizer, drying the doctor bladed sheet, and blanking it into appropriate sized greensheets. Via holes are then mechanically punched for forming electrical interconnections through the sheet. Holes may also be punched in the greensheets to form cavities which will eventually hold the integrated circuit semiconductor device. Electrically conductive paste is deposited in the holes, and in appropriate patterns on the surface of the greensheets, the greensheets stacked and laminated, and the assembly subsequently fired at an appropriate sintering temperature.
There are several methods of forming the cavities in the greensheets. One of these is custom machined punch and die sets. While this method is advantageous for manufacturing large numbers of-parts, the machined punch and die sets are expensive and require long lead times. In addition, this method is inflexible for manufacturing new cavity designs or moderate numbers of parts.
Another method for forming cavities is an energy beam system such as the electron beam system disclosed in Booke et al. U.S. Pat. No. 5,124,522, the disclosure of which is incorporated by reference herein. Here an electron beam is utilized to machine features in a greensheet. These kinds of systems can easily handle design changes but they involve large capital expenses and long process times. Also of interest is the scanning laser drilling system disclosed in LaPlante et al. U.S. Pat. No. 5,168,454, the disclosure of which is incorporated by reference herein. Again, the laser drilling system has great flexibility but is expensive and throughput of the system is a concern.
It would be desirable to have a system that is more flexible, simpler and less expensive to form cavities.
Kumagai Japanese Published Patent Application JP02-139202, the disclosure of which is incorporated by reference herein, discloses a system for punching holes in a greensheet which consists of a bottom plate, die, silicone rubber platen and ram. When a greensheet is placed between the die and platen, and force is applied by the ram, the platen forces portions of the greensheet into the apertures of the die. The platen itself is eventually extruded into the apertures of the die, thereby displacing the portions of the greensheet and forming holes or apertures in the greensheet. While this system is effective, it is not without its problems. For example, rounding of the greensheets rat the holes occurs, i.e., sharp holes are not formed. This rounding is made even worse when thicker greensheets are utilized.
Deshet U.S. Pat. No. 4,856,399, the disclosure of which is incorporated by reference herein, discloses an apparatus very similar to Kumagai above. Deshet, in addition, discloses that the surface of the platen facing the die is heterogeneous in nature, containing localized regions of higher hardness than surrounding areas of the platen. The localized regions of higher hardness aid in the forming of holes with sharper corners in thin sheets. The thin sheets may be metallic or nonmetallic. It is apparent that the sharpness of the holes would depend on the location of the localized regions of higher hardness. In addition, Deshet would still have problems with thicker sheets of material.
Thus, there still remains a need for a punching apparatus and method which are simple in use and flexible in operation that could produce sharp apertures in sheets of material.
Accordingly, it is a purpose of the present invention to have a punching apparatus and method which are simple in use and flexible in operation for making apertures in sheets of material.
It is another purpose of the invention to have a punching apparatus and method for making sharp-cornered apertures in sheets of material.
It is yet another purpose of the invention to have a punching apparatus and method for making sharp-cornered apertures in thin and thick sheets of materials.
These and other purposes of the invention will become more apparent after referring to the following description of the invention considered in conjunction with the accompanying drawings.